Means for increasing the capacity of truck mixer drums



Nov. 8, 1955 R. w. SMITH 2,723,112

MEANS FOR INCREASING THE CAPACITY OF TRUCK MIXER DRUMS Filed Dec. 21,1953 2 Sheets-Sheet 1 Dun-mass HSCHRRG m INVENTOR.

BY ROBERT W. SMlTH ATTORNEY R. W. SMITH MEANS FOR INCREASING THECAPACITY OF TRUCK MIXER DRUMS Nov. 8, 1955 2 Sheets-Sheet 2 Filed Dec.21,v 1953 FIG. 6

FmQ. 5

INVENTOR.

BY Roeemr W. 5mm

ATTORNEY Uited States Patent O MEANS FOR INCREASING CAPACITY OF TRUCKMDQER DRUMS.

Robert W. Smith, Milwaukee, Wis., assignor to The T. L. Smith Company,Milwaukee, Wis., a corporation of Wisconsin This invention relates totruck .type concrete mixers and agitators and particularly to increasingthe capacity of a given size mixer or agitator drum. In increasing thecapacity it is necessary to reduce the weight of the unit in order toremain within the highway weight restrictions obtaining in the severalstates. Therefore, this invention also relates to reducing the weight ofthe mixer unit.

Mixers and agitators have'been customarily provided with a sealing doorat the rear end of the drum to prevent leakage. These doors may beassociated with a charging hopper or the hopper may be omitted in caseswhere hatch loading is employed. The present.invention relates toeliminating the sealing door while preventing leakage past the blades.When the present invention is practiced the level in the drum is limitedonly by the size of the opening, if any, centrally of the blades. Thus,if the charging hopper is retained the level may be raised to the bottomof the opening in the rear of the drum centrally of the blades (withsome allowance for surge, of course); Reduction of the size of thecentral opening allows the level to be raised and if the drum is pluggedcentrally of the blades the level may be raised almost to the extent offilling the drum.

My invention relates, therefore, to the prevention of leakage past theblades, without sealing the end of the drum to allow the capacity to beraised to limits. imposed only by leakage elsewhere. Not only does thisinvention permit the capacity to be raised to almost any desired levelin the drum -but the invention permits elimination of the sealing doorand the attendant maintenance and weight problems. The charging hoppermay also be eliminated, if desired, to effect further weight savingswhich may be utilized in increased capacity. This invention is not,therefore, restricted to any particular construction for preventingleakage centrally of the blades but relates to preventing leakage pastthe blades to permit the drum to be loaded to almost any desired level.a

Other objects and advantages will be pointed out in, or be apparentfrom, the specification and claims, as will obvious modifications of theembodiments shown in the drawings, in which: f

Fig. l is a side elevation with parts broken away and partly in sectionto show the present invention as applied to a mixing drum provided witha charging hopper;

Fig. 2 is a section taken as indicated by line, 22 on Fig. l; v V

Fig. 3 is a view taken as indicated by line 33 on Fig. 1; I I I Fig. 4is a view similar to Fig. l but shows a hatchloaded drum in which thecentral opening at the rear of the drum has been'reduced and thecapacity of the drum has been increased over that of the modificationshown in Fig. l;

Fig. 5 is a section of Fig. 4 taken as indicated by line 55; and I iceFig. 6 is a view taken as indicated by line 6-6 on Fig. 4.

Considering the construction shown through Figs. 1,

2, and 3, first, the drum 10 is of the conventional exterior design andis shown upwardly and rearwardly inclined at the angle it would occupywhen mounted on a mixer or agitator of the high discharge type. Twospiral blades 12, 14 are fixed on the interior of the drum and originateadjacent the open rear end of the drum and terminate adjacent theforward end of the drum. These blades have a T-shaped cross section overa major portion of the drum length since this type of blade greatlyfacilitates the charging and discharging action of the drum. Theso-called charging cone 16 mounted centrally of the blade adjacent theopen rear end of the drum is a modification of the type well known inthis art. These charging cones have been employed in the past tofacilitate rapid charging of the drum. Thus the material was introducedthrough a hopper similar to hopper 18 shown in the drawing pivotallymounted on pin 20 which is fixed on the stationary channel frame member22. Suitable hanger arms or the like may be provided for moving thehopper out of the charging position in which it is shown in the drawingor the hopper may be fixed in position if desired. In the prior art thehopper assembly was generally provided with a sealing door which restedagainst the rim of the drum to seal the contents of the drum during themixing or agitating portion of the operation. The present hopperassembly does not employ the sealing door found in the prior art butprevents leakage between the charging cone and the interior of the drumby means about to be described. I In the prior art the charging cone orfrusto-conical member 16 was so proportioned that its forward edge 24projected into the drum only to the extent that the cone spanned thespace between the terminal edge of a blade and. a point on the otherblade forwardly of the terminal edge of the blade andlying in a planecommon to the terminal edge, the junction point, and the longitudinalaxis of the drum. Thus the rear edge 24 of cone 16 meets blade 14 atpoint 26 which lies in a plane common to the point 26, the terminal edgeof blade 12 at the rear end of the drum, and the longitudinal axis ofthe drum. Put another way, the cone contacted each of the two blades foror 360/N where N is the number-of blades. If the cone 16 in Fig. l wasnot modified and was rotated in the mixing direction the contents wouldspill over at point 26 and run out the rear end of the drum past theterminal edge of blade 12.

In the construction shown in Figs. 1, 2, and 3 I insert a triangularpiece 28 in the form of an axial extension on the rearward edge 24 ofthe cone 16 and T blade 14 to, in effect, create a short spiral tunnelbetween blades 12 and 14. This tunnel starts at point 26 and theterminal edge of blade 12 and extends around to the edge 30 of theinsert piece 28. This insert is welded to the blade and to the cone andthus becomes an integral part of the cone structure. A similar insert 32is fitted between edge 24 and T blade 12 to make a similar tunnel. Thusthe cone is made to contact more than 180 of each blade (or more than360/N) which creates two tunnels. By proper selection of the size of theinsert the tunnel may be made to extend around the drum axis asufiicient number of degrees to prevent leakage past the blades so thatthe only limiting factor on the capacity of the drum is leakagecentrally of the blades. Theoretically, the trailing edge 30 of insert28 or the leading edge of blade 12 should be above a horizontal planepassing throughthe lowest point of the opening centrally of .the drum inall rotational positions of the drum to prevent leakage of the drumcontents past the blades. When this has been accomplished the drumcontents tending to spill over the trailing edge of the insert 28 areprevented from running down the drum wall and out through the openingbetween the cone and'the drum since the opening is blocked by blade 12.If the above prescribed requirements are metthe drum may be filled tothe level of the lowest point of the opening in the cone without leakagetaking place in any rotational position of the drum.

The construction illustrated in Fig. 1 does not meet the aboverequirements strictly since the drum is charged while being rotated inthe mixing or agitating direction and is constantly rotated in thatdirection until theoperator is prepared to discharge the load. Sinceconcrete does not flow readily, when the drum is rotated during loadingit is. only necessary-to make insert 28' of sufficient size to preventthe concrete from flowing between the cone and the drum fast enough toget ahead of the leading edgeof blade 12 before the blade reaches aposition blocking'the flow. This; ofcourse, must take into account therotational speed of the drum but it will be appreciated thatthe insertpiece may be shorter than the theoretical size. In the drawing thespiral tunnel extends about the drum axis approximately'thirty-fiverotational degrees and this construction serves to prevent leakage whilethe drum rotates in the mixing direction. While it is difficult tomathematically set out the exact number of rotational degrees ofnecessary tunnel the existence of the-tunnel is of great importance andwithout the tunnel leakage would most certainly occur. It is, of course,easiest to design for the optimum or theoretical conditions in which theleading edge of blade 12 or the trailing edge of insert 30 is above thehorizontal plane through the bottom of the cone opening in allrotational positions of the drum.

In the modification shown in Figs. 4 through 6 the drum 10 is providedwith a hatch (not shown) located in the cutout portion 34 of the drumfor loading at the central plant. In this modification the cone 36 isprovided-withan integral plate 37 at the rear end having acentralaperture 38 which may be usefully employed as a'vent during thehatch loading of the drum and for inspection of the drum contents duringthe agitating process. Since the diameter of the opening 38 is less thanthe diameter of the open rear end of cone 16 in Fig. l the level withinthe drum can now be raised to the lower edge of opening 38 and thusincreased over the capacity of the modification shown in Figs. 1 through3 without experiencing spillage'centrally of the cone; In order toprevent leakage or spillage past the blades the cone is now extended tospan more of the space between the adjacent blades andthus definetunnels of a greater number of degrees of rotation about the drum axis.Thus, in this modification the tunnel extends'around' the drum axisabout 90 and this extension is sufficientto prevent leakage past theblades even thoughthe level within the drum is up to the bottomedge'of'opening 38 in the end of the cone.

Instead ofproviding-plate 37 on the endof the coneto reduce the size ofthe opening the cone can be sharply tapered so the space between thedrum wall and cone diverges rearwardly. This construction has a'furtheradvantage in'assisting discharge as fully explained in my copendingapplication Ser. No. 399,197.

Although buttwo embodiments of the present invention have beenillustrated and described it will be apparent to those skilled in theart that various other changes and modifications may be made thereinwithout departing from the spirit'of the invention or from the scope ofthe appended claims.

Iclaim:

1-. The: combination with a truck mixer drum of the typehaving an openrear end and including a plurality of circumferentially spaced spiralblades formed on the interiorof the drum and originating at theopenrearend of. the drumandextendingforwardly and terminating adjacent tothe opposite end of the drum, of a member mounted in the rear end ofsaid drum and having a hollow generally frusto-conical portion incontact with the blades at the point of origin thereof, and extendingforward within the drum in continuous contact with eachblade memberspirally toward the opposite end of the drum through arcs of contactsubstantially equal respectively to the arcuate distance betweenadjacent blades whereby the termini of said arcs of contactsubstantially lie respectively in planes passing through the axis of thedrum and through the point of origin of a next adjacent blade,,and. anaxial extension on said frusto-conical member in the region of each saidtermi projecting forwardly into contact with therespectively adjacentspiral blades and extending and maintaining the continuity of the arcsof contact between said frusto-conical member and the respectiveblades,said axial extensions, the frusto-conical member, the innerv surface of:the'drum and the opposing faces of. adjacent spiral blade memberstogether forming spiral tunnels, said tunnels-.each'havin-g an arcuateextent less'than the circumferential distance between adjacentbladeslbut suflicient to prevent leakage of material from the. drumthrough the openendthereof when it is rotated in a direction such thateach said point of origin becomes the leading end of its spiral blade.

2. The combination recited in claim 1 in which the rear end of thefrusto-conical memberhas a central openingand the spiral tunnels are ofsuch length that either the point'of origin of a given blade or theforward terminus of. the tunnel communicating with the forward face ofsaid given blade israt all times above a horizontal plane passingthrough the lowest point of said central opening in the member.

3. The combination with a. truck mixer drum of the type having anopen'rear end and including a plurality of circumferentially spacedspiral blades formed on the interior of the drum and originating at theopen rear end of the drum and extending forwardly and'terminatingadjacent to the oppositeend of thedrum, of a member mounted in-the rearend of. said drum and having ahollow generally frusto-conicaliportion incontact with the blades at the point of-originrthereof. and extendingforwardly therefrom within the drum and in substantially continuouscontact'with each blade: through an arc of contact substantially equalto the arcuate distance between adjacent blades whereby'the" termini of.said arcs of contact substantially lie respectively inplanes passingthrough the axis 'of' the drum and through the point: of origin of anadjacentablade, .saidfrusto-conical vmember having a centralopening,said frusto-conical member in the region of each said termini beingprovided with an axial extension projecting'forwardly'into. contactwiththe respectively adjacent spiral blades. to thereby increase the arcuateextent of contact between said. blades and said frustoconical memberbeyond said termini, said axial extensions together withthefrusto-conical membenthe inner surface of the drum and the opposingfaces of adjacent spiral blade members forming spiral tunnelsextendingcircumferentially beyond said terminiian amount less than thecircumferential.distancebetween adjacent blades but to an extent suchthat either the point of origin of a given blade. or the-forward.terminus of an associated spiral tunnel is always above-ta horizontalplane passing through the lowest point of said opening in thefrusto-conical member whereby to prevent leakage of material from thedrum through the open end of the drum when it is rotated in a directionsuch that each said point of origin becomes the leading end of itsspiral blade.

References Cited in the file-of this patent UNITED STATES PATENTS

